Range-finding apparatus



B. N. WALLIS RANGE-FINDING APPARATUS Filed June 10, 1944 3 Sheets-Sheet1 ,j nzienior M M n QLQ Zf/ Mu Jazz,

Oct. 30, 1945. B. N. WALLIS ,1

RANGEJINDING APPARATUS Filed Jun 10, 1944 a Sheets-Sheet 2 #TTOIVIVE)Get. 30, 1945. B. N. WALLIS 2,388,197

RANGE-FINDING APPARATUS v Filed June 10,1944 3 SheetsSheet 3 v 0 GROUNDvzss PH SPEED d I Patented Oct. 30, 1945 RANGE-FINDING APPARATUS BarnesNeville Wallis, Weybridge, England, as-

signor to Vickers-Armstron-gs- Limited,- -West'-. minstenLondon, England1 Application June 10, 1944, SeriaI No'. 539,719

In Great Britain June 10, 1943 7 Claims. (Cl. 8.8-2.2)

The apparent distance of a target objectfrom an observer, when viewedacross an expanse of water, is deceptive, and the accurate estimation ofranges in such circumstances is a matter of some difficulty for thepilot of a torpedo-carrying aircraft, all the more so because anadditional complication, is introduced by the fact that the range of atarget is constantly closing as th aircraft approaches at high speed.The present invention has for its object to provide an improvedinstrument by means of which the pilot of a torpedo-carrying aircraft,who is able to form a reasonably close estimate of (a) the size of histarget, (b) the angle of inclination of the target to the line ofattack, (6) the direction and speed of the target (it moving across theline of at: tack), (d) the speed of his own aircraft towards the target,and (e) the state of. the water surface (i. e. calm, choppy .or rough),may be enabled to inform himself precisely when the actual.

target distance coincides with the optimum range ofv his projectile, atwhich instant he should endeavour to discharge the same.

An instrument in accordance with the invention comprises two transparentreflecting screens mounted side by side and capable of individualpivotal movement in unison, though in opposite directions, aboutparallel axes, means for operating said transparencies so as to adjusttherdihedral angle between them to a. value supplementary to the knownangle which is subtended at a given range at the observerseye by anobject of known dimension, and means for moditying such dihedral angleto take account of any one or more of the variable conditionshereinbefore referred to.

The instrument is intended to be placed in a convenient position, with aclear view through an aircraft windscreen, so that the observer or pilotmay view the target through the transparent reflecting screens. Thepilot is provided with,

a source of light (which term includes a mirror reflecting a beam from asource of light) fixed above his master-eye in such a positionas, todirect a beam onto each transparent reflecting screen, and itisaccordingly evident, since the reflection of such source of light fromeach transparent reflecting screen must be normal to the plane thereof,that the two reflections will subtend at the pilots eye an angle equalto the angle subtended by the target at the required range and under theconditions of attack which have been previously determined. Whenmakingan attack it is thus merely necessary for-the observer, who haspreviously, adjusted the trans;

parent reflecting, screens of the apparatus, to

note. the instant when the, reflections of such light source in the twotransparent reflecting screens coincide with the. horizontal extremitiesof, the target viewed. through the transparent refleeting; screens andat suchinstant to discharge his projectile. The theoretical basis oftheinvention may be more. easily understood by reference to the. diagram.contained in Figure 1 of'the accompanying. drawings. In. this diagramthe line AB represents the course of an attacking aircraft towards thetarget ship, a plan of which is indicated at C; the course-line AB isdirectly broadside tothe target amidships and the extremities of the,target arev indicated at D and. E- The points P P and P? respectivelydenote the. positionsof the pilot's eye at three successive instantsduring the attack, and, it. should be understood. that the source ,oflight referred to above is practically coincident in position with theeye of the pilot. The, two transparent reflecting screens of theapparatus provided by the invention are indicated at T and T Now itwill'be seen that at position P the lines. along which. thelight-sourceis reflected inthe. transparent reflecting screens T T (indicated bythechain-dotted lines R R include an angle larger than the angle or whichis subtended at the pilots eye by the extremities D, E of the target.Assuming that the dihedral angle between. the transparent reflectingscreens has been pre -adjusted. to suit a given optimum range, takingaccount of such. corrections as may be necessitated by .thevariableconditions previously referred to, it follows that position P istoodistant from. the target for the attack to be made.

, Coming next to position. B? it isseen that the reflections of thelight-source coincide with the sight-lines of'the extremiti'es of thetargetj in other words, the angle p subtended at the pilots eye bythetarget is supplementary to the dihejectile has been passed and that theaircraft is now too close to th target for the ideal attack.

One form of apparatus constructed in accordance with the invention ishereinafter described I being mounted by means of a spherical joint ,7

H, l2 upon a suitable support l3. ,The bracket Ill carries a frame orhousing M which contains.

the mechanical portions of the apparatus and upon the upper side ofwhich are mounted ;two

ally and to some extent circumferentially in relation thereto. The cam22 may be operated independently by means of a lever or finger-piece 3Bwhich is pivoted on the sleeve 28, an ofiset 3! on said lever 33 beingarranged to cooperate With a bifurcated lug on the cam 22, one arm ofwhich lug is indicatedat 222 in Fig.3, in such manner that pivotalmovements of sai'dlever 30 are communicated to the cam 22. It will beseen that the cam 22 is provided with two operative faces, respectivelyindicated at 223 and 224; either'of these faces may be brought intooperative relationship with the cam-follower 21 of V the lever 20 bypushing or pulling the spindle 26 endwise in relation to the housing M,the extent of such endwise movement being limited in one optically flatpanes l5, l6 of glass or other trans parent material, said panes l5, l6being capable of individual pivotal movement about a vertical axisthrough a few degrees on their respective pivots l'l, I8.- The saidpanes I5, IB are supported in channel-shaped members l5l, it! which areextended towards each other so as to overlap as shown in Fig.2. A'connecting pinl9 passes through a hole I52 in the member l5! and a slot162 in the member IBI and the arrangement is such that pivotal movementof one pane, say'the pane I6, is communicated in an opposite sense andto the same degree to the other plane [5, so that thedihedral anglebetween said panes is increased or diminished symmetrically with respectto the central fore and aft axis of the apparatus. The movement of thepanes l5, I6 is effected through the medium of a lever fixed to thepivot l8 of the pane l6, said lever 20 carrying at its extremity acam-follower 2 I which cooperates with the surface of a rotary cam 22.The movement of the'lever 20 in a clockwise direction (as viewed in Fig.3) has the effect of decreasing thedihedral angle between the panes; thereturn movement is achieved by means of a helical spring 23 which isanchored at 24 on the housing l4, "and which bears against a lever 25fixed on the pivot I! of the pane l5 so as to urge the panes l5, l6towards the position in which their dihedral angle is largest.

The various adjustments of the dihedral angle between the panes l5, l6,which are necessary to take account of different target sizes, differentangles of inclination of thetarget to the line of attack, differentdirections and speeds of the target (if moving across the line ofattack), different speeds of the attacking aircraft and different watersurface conditions, are effected through the medium of a series ofeccentrics and cams the operation whereof actuates the pane Hi throughthe lever 20. The mechanism comprises an inner spindle 26 which isrotatably mounted in the front and rear Walls'of the housing l4, andwhich bears a knob 21 on its foremost extremity. Upon an eccentricsheave-portion 26! of the spindle 26 is rotatably mounted aneccentrically bored sleeve 28, carrying at its foremost extremity alever or finger-piece 29 which projects laterally at the left-hand sideof the instrument. Thesleeve 28 in turn carries the cam 22 hereinbeforereferred to which is rotatable on the sleeve 28 and which is providedwith acannelure 22| which cooperates with a peg 2'62 on the spindle 26in such manner that on endwise movement of the latter a correspondingaxial movement may be communicated to said cam- 22. The sleeve 28 is cutaway at'28l to accommodate the movement of said peg 262 both amdirectionby the abutment of the knob 21 against the face-plate 3| (hereinafterreferred to) and in the other direction by the abutment of the collar263 against the back of the housing 14.

The angle which will be subtended by a target object at theobserver's-eye at a known range being exactly calculable, it isnecessary to provide a primary adjustment'of the panes 15, I6 for thepurposeof setting them initially at a dihedral angle supplementary totheknown angle which will be subtended by atarget of-known size (i e.horizontal dimension) at the intended range. This iseifected by rotatingthe cam 22 by means of the lever 30.- As will be seen from Fig. 5, saidlever 3 O-isarranged to register with one of a plurality of calibratedtarget sizes marked on the face-plate 3|. The position of the lever 30illustrated in Fig. 5 is appropriate to a target ship'of 600 feetoverall length. The lever 30 should be raised to suit a larger targetand depressed in" the case of a target of smaller horizontal dimensions.

Where the effective range of the missile is dependent upon the state ofthe water surface, so that choppy or rough conditions have the effect ofdecreasing the range as compared with a calm surface, a secondaryadjustment of the cam 22 may be effected by using either of the twofaces 223, 224 thereof, theappropriate one of these being selected bypushing" in or pulling out the knob 21. The face of the knob 21conveniently bears the'legend Rough'SeaPush; Calm Sea -Pull, as showninFig. 5. When the spindle 26 is pushed inwardly, to bring the surface224 into operative'relationship with the cam-follower 2! of the lever20, the panes l5, I6 are set at a smaller dihedral angle, giving ashorter-range, than when the knob 21 is pulled out to bring thecam-surface 223 under'the cam-follower 2|, for

calm sea conditions. j i

' When the target is inclined to the line, of attack, so as to appearforeshortened, the settin of the panes I5, l6 must be modified inproportion to the angle of'such inclination. This adjustment'is obtainedbyrotating the knob 21 until it assumes an'attituderoughly correspondingto that presented by the target, the consequent rotation of the spindle26having the effect of moving the cam 22 "bodily from the datum positioneither 'to the right or to the left, which movement is communicatedthrough the lever 20 to the panes l5, I6. I

The speed of the projectile will be affected by the relative groundspeed of the aircraft from which it is discharged; The dihedral anglebetween the p-anes l5, l6 is'accordingly increased proportionately asthe aircraft ground speed is increased, thus-preserving the optimumvelocity/range ratio'for the projectile, by adjusting answer theposition of the Elector 29 which "the angular position about its .axisor thcaeccentric sieevej28, 'Such'wariation ris efiectivewto modify theposition of the cam 22 toseither side ofithc datum position. As will be:iseen ,from Fig; it the face-plate 3| -bears a series :of speed mark:ings, graduated around its lettehand edge, inrelation to which markings:the lever {29 i581 Where, in the case of an attack upon a target movingacross the line :of attack, it is possible for the observer to-estimatethe speed Df the target, he may, by rotating the whole instrument uiponits support 13, adjust the apparatus according to the requisite degreeof lay-01f --to :port or star board. A wing-nut 32 is provided forfixing-the instrument at the requisitelay-ofi ,position. H

The reference -nurneral-33 r-indicates a smokedglass screen which mayberaised to and fixed in the position shown in chain-dotted lines in Figs.4 and 5, to prevent dazzle when flying towards the sun, the nut 34 beingprovided to fix the screen 33 in the required position.

The apparatus provided by the invention is characterised by aconsiderable degree of tolerance. For example, its accuracy is notseriously affected by the position of the observers head in relation tothe panes l5, 16 in a fore-and-aft direction, since the extent of hishead movement in that direction is infinitesimal in comparison with therange distance. Side to side movements of the observers head make nodifference whatever, so long as he is able to retain his master-eye viewof the extremities of the target through the panes l5, [6.

The source of light required to provide the reflections in the panes [5,I6, which the observer must align with the extremities of the targetwhen using the instrument, is conveniently, provided by a small electricpea-lamp fitted to a harness or frame fixed to the observers helmet in aposition immediately above his master-eye, and the resultant reflectionstake the form of a spot seen in each pane. Since, however, the observermay experience some difliculty in adjusting the vertical elevation ofthe spots of light to coincide with the extremity of the target as seenthrough the panes l5, IS, with corresponding uncertainty as to theprecise instant at which coincidence of length of target with thedistance between the spots occurs, it is desirable to provide animproved transparent reflecting screen for the panes I5, l6 whereby thereflection of the source of light appears, not as a single spot, but asa line of light across the pane, so that the two lines of lightappearing in both panes may serve as the limits of a frame by which theview of the target is outlined.

It is found that when a transparent reflecting screen is polished insuch a manner as t produce a very large number of closely pitchedparallel lines on its surface the reflection from a single point oflight is seen as a line, and the faces of the transparent reflectingscreens forming the panes I5, l6 are accordingly polished with a uniformrectilinear motion in such a manner as to produce a line of light inplace of the aforesaid single spot. To produce a vertical line thedirection of motion in polishing is horizontal.

The bracket in may be adjusted upon its spherical mounting ll, l2 sothat the principal reflections of the source of light from the meanplanes of the panes I5, l6 do not enter the observers eye, the resultantlines alone being visible. In this manner a frame is produced which,without distracting the attention of the observer, accurately outlinesand defines the position of the extremities i i Mb i,...\ l l' 11; willbe evident that'the" apparatusis equally suitable for; the ranging mi'targetsli which are more conveniently defined by ayerticalthninl'by ahorizontal dimension, tor; rtheiapparalius lbe so (disposed that theipivot-zaxesrof the panes .l 5, Hi be horizontal finstead of werticazl,:anda'fithe polishing motion be married snout in ,a":verti-calrdisrection, twin horizontal lines will zappeamto which allthe adjustments mreviously describedcmayxbe applied with a view toaltering the MED-tidal dis: tance between them insuch .aimannenasstodie-.- fine the requiredjrange. This arrangementihas the additionaladvantage thatiit ispossiblezto omit, the adjustment, f ,the transparentrefleote ing screens to 'lallow, ionanangular approach rte the target,since the extreme dimension of an object, such as a funnel or a mast ofa ship, is unchanged by foreshortening 'at oblique angles of attack,

What I claim as my invention and desire to secure by Letters Patent is:

1. An instrument for use on an aircraft approaching a target forindicating the optimum target range at which a torpedo should be firedcomprising two transparent reflecting screens through which an observerviews the extremities of the target, said screens being mounted side byside andcapable of individual pivotal movement in unison about parallelaxes but in opposite directions, means for operating said screens so asto adjust the dihedral angle between them to a value supplemental to theknownangle which is subtended at a given range at the observers eye byan object of known dimension, and means for varying said dihedral angleto take into account the ground speed of the aircraft, the inclinationof the target relative to the line of sight and the ot the target atithefirequimd 40 condition of the sea, whereby light from a sourceadjacent the eye of the observer is reflected by said screens to providemarks which come into coincidence with the extremitiesof the target asviewed through said screens when said optimum range is reached.

2. An instrument as claimed in claim 1 wherein said screens consist ofoptically fiat glass panes, and comprise means constraining the panes topivot simultaneously in opposite directions to the panes toward a datumposition, and a series of independently operable cams associated withone of said panes in such manner that any one thereof may be actuated toadjust the panes in relation to said datum position.

3. An'instrument as claimed in claim 1 comprising means constrainingsaid screens to pivot simultaneously in opposite directions to the sameextent, a series of independently operable cams associated with one ofsaid screens in such manner that any one thereof may be actuated toadjust the dihedral angle between said screens, a setting memberassociated with each of said cams, and scales respectively registeringthe positions of said setting members in accordance with the desiredadjustments of said angle.

4. An instrument as claimed in claim 1 comprising a frame on which saidscreens are pivotally mounted, means constraining said screens to pivotsimultaneously in opposite directions to the same extent, a spindlerotatable in said frame and provided with an eccentric sheave-portion,an eccentrically bored sleeve rotatable on said sheave-portion, a camrotatable on said eccentric sleeve, separate means for rotating saidspindle,

same extent, spring means resiliently urging both sleeve and camindividually, and a cam follower cooperating with said cam and connectedwith one of said screens whereby the rotation of any one of saidspindle, sleeve and cam produces a pivotal movement of said screens toadjust the dihedral angle between them. I 5. An instrument as claimed inclaim 1 com prising a frame on which said screens are pivotally mounted,means constraining said screens to pivot simultaneously in oppositedirections to the same extent, a spindle rotatable in said frame andprovided with an eccentric sheave-portion, an eccentrically bored sleeverotatable on said sheave-portion, a cam rotatable on said eccentricsleeve, separate means for rotating said spindle, sleeve and camindividually, a cam follower cooperating with said cam and connectedwith one of said screens whereby rotation of any one of said spindle,sleeve and. cam produces a' pivotal movement of said screens to adjustthe dihedral angle between them, said cam being provided with axiallyspaced working faces, and means for moving the cam axially relative tothe spindle and sleeve so as to select a desired cam face forcooperation with said follower. I

6. An instrument as claimed in claim '1 comprisingmeans for rotatablymounting the instrument as a whole about a vertical axis to effectadjustment for lay-off.

'7. An instrument as claimed in claim 1 having screens polished with auniform rectilinear motion whereby the reflection of the light sourceappears as a line across the screen.

BARNES NEVILLE WALLIS.

